KR20160027114A - Injection molding machines and methods for accounting for changes in material properties during injection molding runs - Google Patents

Abstract

The method and machine take into account changes in material properties of the molten plastic material during injection run. A change in the control signal is calculated by the controller during injection molding operation. When the change in the control signal indicates a change in material flowability, the controller alters the target injection pressure to ensure that the molten plastic material completely fills and packs the mold cavity to prevent component defects such as short shot or flashing.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine and an injection molding machine, and more particularly, to an injection molding machine and method for considering changes in material properties during injection molding operation.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine and method for manufacturing an injection molded part and more particularly to an injection molding machine and method for manufacturing an injection molded part by controlling the operating parameters of an injection molding machine during an injection molding run, And a method for considering changes in injection molding material properties during injection molding operations.

Injection molding is a commonly used technique for the mass production of parts made of meltable materials, most commonly parts made of thermoplastic polymers. During repetitive injection molding processes, plastic resins, most often in the form of small beads or pellets, are introduced into an injection molding machine which melts resin beads under heat, pressure, and shear. The molten resin is now forcibly injected into a mold cavity having a specific cavity shape. The injected plastic is retained under pressure in the mold cavity, cooled, and then removed as a solidified component having a shape essentially replicating the cavity shape of the mold. The mold itself may have a single cavity or multiple cavities. Each cavity can be connected to the flow channel by a gate that directs the flow of molten resin into the cavity. The molded part may have more than one gate. It is common for large components to have two, three, or more gates in order to reduce the flow distance that the polymer must travel to charge the molded part. One or more gates per cavity may be located anywhere on the part geometry, may have any cross-sectional shape such as essentially circular, or may be shaped to have an aspect ratio of 1.1 or greater. Thus, a typical injection molding procedure involves four basic operations: (1) heating the plastic in an injection molding machine to allow the plastic to flow under pressure; (2) injection of molten plastic into mold cavities or cavities defined between two closed mold halves; (3) allowing the plastics to be cooled and cured in cavities or cavities under pressure; And (4) opening mold halves and discharging the components from the mold.

During the injection molding process, the molten plastic resin is injected into the mold cavity and the plastic resin is forcibly injected into the cavity by means of an injection molding machine until the plastic resin reaches a position in the cavity farthest from the gate. Thereafter, the plastic resin charges the cavity from the end toward the gate again. The resulting length of the part and wall thickness are the result of the shape of the mold cavity.

In some cases, it may be desirable to reduce the plastic content of the finished part, and thus the wall thickness of the injection molded part to reduce cost. Reducing wall thickness using conventional variable high pressure injection molding processes can be an expensive and uncommon challenge. Indeed, a conventional injection molding machine (e.g., a machine that injects molten plastic resin from about 8,000 psi to about 138,000 psi (20,000 psi)) is capable of forming a thin wall of a part Have practical limitations. Generally speaking, conventional injection molding machines can not mold parts with thinwall ratios greater than about 200 (as defined by the L / T ratio described below). Moreover, molding thin wall components with a thin wall ratio of greater than 100 requires a pressure at the top of the current capability and therefore a pressure capable of handling such high pressure.

When charging thin wall components, current industrial practice is to fill the mold cavity with the highest possible speed that the molding machine can achieve. This approach ensures that the mold cavity is filled before the polymer solidifies or "hardens " in the mold and provides the lowest possible cycle time because the polymer is exposed to the cooled mold cavity as quickly as possible. This approach has two drawbacks. The first is that achieving very high charging rates requires very high output loads, which requires very expensive molding equipment. In addition, most electrical presses require very complex and costly drive systems that either can not provide sufficient power to achieve such high fill rates, or significantly increase the cost of molding equipment, making them economically impractical.

A second drawback is that high charging speeds require very high pressures. This high pressure creates the need for a very high clamping force to keep the mold closed during charging, and this high clamping force results in very expensive molding equipment. The high pressure also requires an injection mold core made from a very high strength material, typically a hardened tool steel. These high strength molds are also very expensive and may not be economically viable for many molded components. Despite these significant drawbacks, the need for thin wall injection molded components is still high, because these components use less polymer material to form the molded part, thereby offsetting higher equipment costs This leads to a reduction in the amount of material remaining. In addition, some molded components require a very thin design element, such as a design element that needs to be bent, or a design element that must match a very small feature of another design element, to perform properly.

As the liquid plastic resin is introduced into the injection mold in a conventional injection molding process, the material adjacent to the cavity walls immediately "hardens ", solidifies or begins to harden, or in the case of crystalline polymers the plastic resin begins to crystallize Because the liquid plastic resin is cooled to a temperature below the non-flow temperature of the material and portions of the liquid plastic are stopped. This plaster material adjacent to the wall of the mold narrows the flow path through which it travels as the thermoplastic material progresses to the end of the mold cavity. The thickness of the layer of coagulated material adjacent the wall of the mold increases as the filling of the mold cavity progresses, resulting in a gradual decrease in the cross-sectional area through which the polymer must flow to continue filling the mold cavity. As the material solidifies, it also contracts and separates from the mold cavity wall, which reduces effective cooling of the material by the mold cavity wall. As a result, conventional injection molding machines maintain the packing pressure to rapidly fill the mold cavity with plastic and then press the material outwardly against the sides of the mold cavity to improve cooling and maintain the correct shape of the molded part . Conventional injection molding machines typically have a cycle time comprised of about 10% injection time, about 50% packing time, and about 40% cooling time.

As the plastic solidifies within the mold cavity, conventional injection molding machines increase the injection pressure (to maintain a substantially constant volumetric flow rate due to the smaller flow cross-sectional area). However, increasing the pressure is disadvantageous in terms of both cost and performance. As the pressure required to mold the component increases, the molding equipment must be strong enough to withstand additional pressure, which is generally equivalent to being more expensive. Manufacturers may have to purchase new equipment to accommodate this increased pressure. Thus, a reduction in the wall thickness of a given part can result in significant capital expenditure to achieve manufacturing through conventional injection molding techniques.

In an effort to avoid some of the aforementioned drawbacks, many conventional injection molding operations use shear-thinning plastic materials to improve the flow characteristics of the plastic material into the mold cavities. As shear-thinned plastic material is injected into the mold cavity, the shear forces generated between the plastic material and the mold cavity wall tend to reduce the viscosity of the plastic material, allowing the plastic material to flow more freely and easily into the mold cavity do. As a result, it is possible to fill the thin wall components quickly enough to avoid the material becoming completely hardened before the mold is completely filled.

The decrease in viscosity is directly related to the magnitude of the shear force generated between the plastic material and the supply system and between the plastic material and the mold cavity wall. Thus, manufacturers of such shear-thinning materials and operators of injection molding systems are increasing their shear so as to increase the injection molding pressure in an effort to reduce viscosity. Typically, high power injection molding systems (e.g., grade 101 and grade 30 systems) inject plastic materials into mold cavities, typically at melt pressures of at least 15,000 psi (103 MPa). The manufacturer of the shear-thin plastic material teaches the injection molding operator to inject the plastic material into the mold cavity in excess of the minimum melt pressure. For example, polypropylene resins are typically processed at pressures greater than 6,000 psi (the recommended range from polypropylene resin manufacturers is typically from greater than 6,000 psi to 15,000 psi) being). Press makers and process engineers typically use a range of temperatures to achieve maximum possible shear thinning and better flow characteristics from plastic materials to achieve maximum possible shear thinning - typically above 15,000 psi (103 MPa) It is recommended that the shear thinning polymer be processed at an upper limit or significantly higher. Shear thinning thermoplastic polymers are typically processed in the range of greater than 6,000 psi (41 MPa) to about 30,000 psi (207 MPa). Despite the use of shear thinning plastics, there is a practical limit to the variable high pressure injection molding of thin walled components. These limits are within the range of the thin wall components with a current thin wall ratio of 200 or more. Moreover, parts with thin wall ratios of 100 to 200 can also be very costly, since these parts generally require an injection pressure of about 15,000 psi to about 20,000 psi to be.

Mass production injection molding machines (i.e., grade 101 and grade 30 molding machines) that produce thin walled consumer products use only molds having the majority of molds made from high hardness materials. Mass production injection molding machines typically experience more than 500,000 cycles per year. Industrial quality production molds should be designed to withstand over 500,000 cycles per year, preferably over 1,000,000 cycles per year, more preferably over 5,000,000 cycles per year, and even more preferably over 10,000,000 cycles per year. These machines have multiple co-molds and complex cooling systems to increase the production rate. High hardness materials are better able to withstand repeated high pressure clamping operations than materials with lower hardness. However, high hardness materials, such as most tool steels, have a relatively low thermal conductivity of less than about 0.3 BTM / HRC (20 BTU / HRFTF), which means that heat is transferred from the molten plastic material through the high hardness material Resulting in a long cooling time.

Despite the ever-increasing injection pressure range of conventional variable high-pressure injection molding machines, there is still a need for an actual (approximately 200 L / T ratio) injection molding machine for molding thin wall components in a conventional variable high pressure (e.g., 138 MPa (20,000 psi) There is still a limit and thin wall components with a thin wall thickness ratio of from about 100 to about 200 can be very costly to many manufacturers.

Changes in molding conditions can significantly affect the properties of the molten plastic material. More specifically, a change in environmental conditions (such as a change in temperature) may increase or decrease the viscosity of the molten plastic material. If the viscosity of the molten plastic material changes, the quality of the molded part may be affected. For example, if the viscosity of the molten plastic material increases, the molded part may experience a short shot, or a shortage of molten plastic material. On the other hand, if the viscosity of the molten plastic material decreases, the molded part can experience flashing because the thinner molten plastic material is pressed into the septum of the mold cavity. In addition, the recycled plastic material mixed with the original material can change the melt flow index (MFI) of the combined plastic material. Conventional injection molding machines do not regulate operating parameters to account for these changes in material properties. As a result, conventional injection molding machines can produce lower quality parts, which must be removed during the quality control inspection, leading to inefficiency of operation.

It is an object of the present invention to provide an injection molding machine and method for considering changes in material properties during injection molding operation.

A method of automatically adjusting an injection molding process to compensate for changes in flowability of a molten plastic material, the method comprising: providing an injection molding machine having at least one mold cavity; The method comprising: providing an injection molding controller comprising a pressure control output configured to provide a control signal to at least partially determine an injection molding pressure for an injection molding process of the injection molding machine,

The method comprises:

Measuring a first control signal from the pressure control output at a first time during an injection molding cycle; Measuring a second control signal from the pressure control output at a second time in the injection molding cycle subsequent to the first time; Comparing the first control signal from the pressure control output and the second control signal from the pressure control output to obtain a comparison result; And at a third time subsequent to the second time, determining a third control signal for the pressure control output based at least in part on the comparison result. do.

The embodiments disclosed in the drawings are illustrative and exemplary in nature and are not intended to limit the subject matter defined by the claims. BRIEF DESCRIPTION OF THE DRAWINGS The following detailed description of an exemplary embodiment may be understood when read in conjunction with the following drawings, wherein like structure is indicated with like reference numerals.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a schematic diagram of an injection molding machine constructed in accordance with the present invention.
Figure 2 illustrates one embodiment of a thin walled part formed in the injection molding machine of Figure 1;
Figure 3 is a graph of the joint pressure versus time for the injection molding machine of Figure 1 overlaid on a joint pressure versus time graph for a conventional injection molding machine.
FIG. 4 is a graph of another cavity pressure versus time for the injection molding machine of FIG. 1 overlaid on a common pressure versus time graph for a conventional injection molding machine, and these graphs illustrate the percentage of charge time required for a given charge step.
5a-5d are side cross-sectional views of a portion of a thin wall mold cavity in various filling stages by a conventional injection molding machine.
6A-6D are side cross-sectional views of a portion of a thin wall mold cavity in various filling stages by the injection molding machine of FIG.
Figure 7 is a schematic view of an injection molding cycle that can be performed on the injection molding machine of Figure 1;
8 is a graph of pressure versus time for an injection molding machine illustrating the effect of changes in viscosity of a molten plastic material.
9A is a graph illustrating changes in control signal voltage over time during an injection molding cycle.
9B is a graph illustrating changes in the control signal voltage over a shifted distance to a melt transfer machine component.
10 is a logic diagram illustrating an injection molding process that takes into account viscosity changes of a molten plastic material;
Figure 11 is a schematic diagram of a control system that may be used to implement the logic diagram of Figure 10;

Embodiments of the present invention generally relate to systems, machines, products, and methods for producing articles by injection molding, and more particularly to systems, articles, and articles for manufacturing articles by injection molding at low, And methods. However, the apparatus and method for considering viscosity changes of the molten plastic material described herein are not limited to injection molding machines and injection molding processes at low, substantially constant pressures. Rather, the disclosed apparatus and methods for considering viscosity changes of the molten plastic material can be used in virtually any injection, including but not limited to high pressure processes, low pressure processes, variable pressure processes, and constant or substantially constant pressure processes Molding machine or an injection molding process.

The term "low pressure" as used herein with respect to the melt pressure of a thermoplastic material means a melt pressure of no more than 15,000 psi (103 MPa) near the nozzle of the injection molding machine.

The term "substantially constant pressure" as used herein with respect to the melt pressure of a thermoplastic material means that the deviation from the reference melt pressure does not produce a significant change in the physical properties of the thermoplastic material. For example, "substantially constant pressure" includes, but is not limited to, pressure fluctuations that prevent the viscosity of the molten thermoplastic material from changing significantly. In this regard, the term "substantially constant" includes a deviation of approximately 30% from the reference melt pressure. For example, the term "substantially constant pressure of about 4600 psi" refers to a pressure of about 41 MPa (6000 psi) (30% higher than 32 MPa (4600 psi)) to about 32 MPa (30% less than 4600 psi). The melt pressure is considered to be substantially constant as long as the melt pressure varies from 30% below the mentioned pressure.

The term "melt holder " as used herein refers to that portion of an injection molding machine that contains molten plastic in fluid communication with a machine nozzle. The melt holder is heated so that the polymer can be prepared and maintained at the desired temperature. The melt holder is connected to a power source, for example a hydraulic cylinder or an electric servomotor, which can be controlled to communicate with the central control unit and advance the diaphragm to press the molten plastic through the machine nozzle. The molten material then flows into a mold cavity through a runner system. The melt holder may be cylindrical in cross section or it may have an alternative cross-section that allows the diaphragm to press through the machine nozzle under pressure that may range from a pressure as low as 100 psi to as high as 40,000 psi . The diaphragm may optionally be integrally connected to a reciprocating screw having a flight designed to plasticize the polymeric material prior to injection.

The term "high L / T ratio" generally refers to an L / T ratio of 100 or more, and more specifically to an L / T ratio of 200 or more, but less than 1000. The calculation of the L / T ratio is defined below.

The term "peak flow rate " generally refers to the maximum volumetric flow rate as measured at a machine nozzle.

The term "peak injection velocity" generally refers to the maximum linear velocity at which the injection ram travels in the process of pressurizing the polymer into the feed system. The ram may be, for example, a reciprocating screw in the case of a single-stage injection system or a hydraulic ram in the case of a two-stage injection system.

The term "ram speed" generally refers to the linear velocity at which the injection ram moves in the process of pressing the polymer into the feed system.

The term "flow rate " refers generally to the volume flow rate of a polymer as measured at a machine nozzle. This flow rate can be calculated based on the ram speed and the cross sectional area of the ram, or can be measured by a suitable sensor located in the machine nozzle.

The term " cavity percent charge "generally refers to the percentage of voids filled on a volumetric basis. For example, when the cavity is 95% filled, the total volume of the filled mold cavity is 95% of the total volume of the cavity of the mold.

The term "melt temperature" generally refers to the temperature of the polymer held in the melt supply system when the hot runner system is used to hold the melt in the melt holder and in the melted state. It is understood that the melt temperature varies with the material, but the desired melt temperature is generally within the range recommended by the material manufacturer.

The term "gate size" generally refers to the cross-sectional area of the gate formed by the intersection of the runner and the mold cavity. In the case of a hot runner system, the gate is either an open design without a definite cut-off of the flow of material at the gate, or a closed design, typically used to mechanically block the flow of material into the mold cavity through the gate Lt; / RTI > The gate size refers to the cross-sectional area, for example a 1 mm gate diameter refers to the cross-sectional area of the gate equal to the cross-sectional area of the gate with a 1 mm diameter at the point where the gate meets the mold cavity. The cross section of the gate can be of any desired shape.

The term "effective gate area" generally refers to the cross-sectional area of the gate corresponding to the intersection of the material flow channel and the mold cavity of the supply system (e.g., runner) supplying the thermoplastic material to the mold cavity. The gate may or may not be heated. The gate may be circular or of any cross-sectional shape suitable for achieving the desired flow of thermoplastic material into the mold cavity.

The term " increase ratio "generally refers to the mechanical advantage that the injection power source has for the injection ram that presses the molten polymer through the machine nozzle. In the case of a hydraulic power source, it is typical that the hydraulic piston will have a mechanical magnification of 10: 1 compared to the injection ram. However, the mechanical magnification may range from much lower mechanical ratio such as 2: 1 to much higher mechanical magnification such as 50: 1.

The term "peak output" generally refers to the maximum output produced when charging the mold cavity. The peak output may occur at any point within the charge cycle. The peak power is determined by the plastic pressure as measured at the machine nozzle, multiplied by the flow rate as measured at the machine nozzle. The output is calculated by the equation P = p * Q, where p is the pressure and Q is the volumetric flow rate.

The term "volumetric flow rate " generally refers to a flow rate as measured at a machine nozzle. This flow rate can be calculated based on the ram speed and the cross sectional area of the ram, or can be measured by a suitable sensor located in the machine nozzle.

The terms "filled" and "full" are interchangeable when used in reference to a mold cavity comprising a thermoplastic material, and both terms mean that the thermoplastic material has stopped flowing into the mold cavity.

The term "shot size" generally refers to the volume of polymer that is ejected from the melt holder to fully fill the mold cavities or cavities. The shot size volume is determined based on the temperature and pressure of the polymer in the melt holder just prior to injection. In other words, the shot size is the total volume of molten plastic material injected into the stroke of the injection molding ram at a given temperature and pressure. The shot size may include injecting the molten plastic material into one or more injection cavities through one or more gates. Shots of molten plastic material may also be prepared and injected by one or more melt holders.

The term "hesitation " generally refers to a point at which the velocity of the flow front is minimized to allow a portion of the polymer to begin falling below its non-flow temperature and begin to harden.

The term " electric motor "or" electric press "includes both an electric servomotor and an electric linear motor as used herein.

The term "peak output flow coefficient" refers to a normalized measure of the peak output required by an injection molding system during a single injection molding cycle, and the peak output flow coefficient can be used to directly compare the output requirements of different injection molding systems . The peak output flow coefficient is first calculated by determining the peak output corresponding to the maximum value of the molding pressure multiplied by the flow rate during the charge cycle (as defined herein), and then determining the shot size for the mold cavity to be filled. The peak output flow coefficient is then calculated by dividing the peak output by the shot size.

The term "low constant pressure injection molding machine" is defined as a class 101 or grade 30 injection molding machine using a substantially constant injection pressure of less than 15,000 psi (103 MPa). Alternatively, the term "injection molding machine with low constant pressure" is made up of first and second mold parts defining a mold cavity between mold cores (using a substantially constant injection pressure of less than 15,000 psi) More than one million cycles, more preferably more than two million cycles, more preferably more than five million cycles, and much more before the end of its useful life, Preferably an injection molding machine capable of performing a cycle exceeding 10 million times. A feature of a "low constant pressure injection molding machine" is that it has a mold cavity with an L / T ratio greater than 100 (and preferably greater than 200), a plurality of mold cavities (preferably four mold cavities, More preferably 64 mold cavities, more preferably 64 mold cavities, more preferably 128 mold cavities, and more preferably 256 mold cavities, or 4 to 512 arbitrary number of mold cavities, more preferably 32 mold cavities, more preferably 64 mold cavities, Mold cavity), a heated runner, and an inductive drain mechanism.

The term "useful life" is defined as the expected life of a mold part before breaking or a scheduled replacement. The term "useful life" when used in connection with a mold part or mold core (or any part of a mold that defines a mold cavity) refers to a problem with respect to the integrity of the mold part, (E.g., fatigue fracture or fatigue crack) occurs in the mold part, before the mold part (s), the galling, the deformation of the parting line, the deformation or excessive wear of the shut- Means the time that a part or mold core is expected to be used. Typically, the mold part reaches the end of its "useful life" when the contact surface defining the mold cavity is to be discarded or replaced. The mold part may require repair or regeneration from time to time over the "useful life" of the mold part, and such repair or regeneration does not require complete replacement of the mold part to achieve acceptable molded part quality and molding efficiency . Furthermore, it is possible that the part is not properly removed from the mold and the mold is forcibly closed on the unreleased part, or the mold part is damaged by the operator using a wrong tool to remove the molded part, It is possible for damage not related to the normal operation of the mold part to occur with respect to the mold part. For this reason, spare mold parts are sometimes used to replace these damaged components before they reach the end of their useful life. Replacement of mold parts due to damage does not change the expected useful life.

The term "inductive exhaust mechanism" is defined as a dynamic component that operates to physically eject a molded part from a mold cavity.

The term "coating" refers to a material having a major function (for example, a function of protecting the material defining the mold cavity, or a function of protecting the mold cavity from the mold cavity), which is located on the surface of the mold component defining the mold cavity. And a function to reduce friction between the molded part and the mold cavity wall to improve removal of the molded part).

The term "average thermal conductivity" is defined as the thermal conductivity of any material that constitutes a mold cavity or mold side or mold part. The materials constituting the coating, the stack plate, the support plate, and the gate or runner-whether integral with the mold cavity or separated from the mold cavity-are not included in the average thermal conductivity. The average thermal conductivity is calculated based on volume weighting.

The term "effective cooling surface" is defined as the surface on which heat is removed from the mold part through it. An example of an effective cooling surface is a surface that defines a channel for the cooling fluid from the active cooling system. Another example of an effective cooling surface is the outer surface of a mold part where heat is dissipated into the atmosphere through it. The mold part may have more than one effective cooling surface and thus a unique average thermal conductivity between the mold cavity surface and each effective cooling surface.

The term "nominal wall thickness" is defined as the theoretical thickness of the mold cavity when the mold cavity is made to have a uniform thickness. The nominal wall thickness can be approximated by an average wall thickness. The nominal wall thickness can be calculated by integrating the length and width of the mold cavities filled by individual gates.

The term "average hardness" is defined as the Rockwell hardness for any material or combination of materials within a desired volume. Where more than one material is present, the average hardness is based on the volume weighted percentage of each material. The average hardness calculations include hardnesses for the materials that make up any part of the mold cavity. Average hardness calculations do not include materials that make up the support plate, whether integrated with the coating, stack plate, gate or runner-mold cavity, or not. Generally, the average hardness refers to the volume weighted hardness of the material in the mold cooling zone.

The term "mold cooling zone" is defined as a certain volume of material that lies between the mold cavity surface and the effective cooling surface.

The term " cycle time "or" injection molding cycle "is defined as a single iteration of the injection molding process required to fully form an injection molded part. The cycle time or injection molding cycle includes advancing the molten thermoplastic material into the mold cavity, substantially filling the mold cavity with the thermoplastic material, cooling the thermoplastic material, separating the first and second mold sides, Exposing the thermoplastic material, removing the thermoplastic material, and closing the first and second mold sides.

The term " injection molding operation " includes a series of sequential injection molding cycles that are performed on a common injection molding machine, as used herein.

The term "flowability" as used herein refers to the flow resistance of a molten plastic material as it flows through an injection molding system, such as the composition, temperature, shear, All influences on the relative viscosity of the molten plastic material, including, but not limited to, design, and part design.

The term "flow factor" is defined as the ratio of the control signal for the proportional valve to the incremental period. This ratio can be expressed in voltage / time units, for example in millivolts / microseconds. This ratio can be determined for any type of injection press (e.g. hydraulic press or electric press) and can be calculated by the formula FF = (CS1-CS2) / T, where CS1 and CS2 are incremental And is a control signal measured over a period of time.

The term "viscosity index" is defined as the ratio of the control signal for a proportional valve to a given travel distance for a melt transfer machine component, such as an injection screw, in an injection molding machine. This ratio can be expressed in units of voltage / distance, for example in millivolts / micron. This ratio can be determined for any type of injection press (e.g. hydraulic press or electric press) and can be calculated by the formula VCI = (CS1 - CS2) / S, where CS1 is the first control CS2 is the second control signal, and S is the travel distance for the melt transfer machine component.

The term "proportional valve" is defined as a valve that moves in proportion to the electronic control signal. For example, if the electronic control signal increases by 10%, the proportional valve will be opened to allow 10% more material to flow through the valve.

Injection molding machines of low constant pressure are also known from U.S. Patent Application No. 13 / 601,514, filed August 31, 2012, which is hereby incorporated herein by reference in its entirety, which may be used to make thin walled consumer products such as toothbrush handles and razor handles (E.g., a grade 101 or grade 30 injection molding machine, or "ultra-high productivity molding machine"), such as the high productivity injection molding machine disclosed in US Pat. Thin-walled components are generally defined as having a high L / T ratio of 100 or greater.

Referring in particular detail to the drawings, FIG. 1 illustrates an exemplary low constant pressure injection molding apparatus 10 generally including an injection system 12 and a clamping system 14. A thermoplastic material may be introduced into the injection system 12 in the form of a thermoplastic pellet 16. The thermoplastic pellets 16 may be placed in a hopper 18 that feeds the thermoplastic pellets 16 into the heated barrel 20 of the injection system 12. [ The thermoplastic pellets 16 may be driven into the end of the barrel 20 heated by the reciprocating screw 22 after being fed into the heated barrel 20. Heating of the heated barrel 20 and compression of the thermoplastic pellets 16 by the reciprocating screw 22 cause the thermoplastic pellets 16 to melt and form the molten thermoplastic material 24. The molten thermoplastic material is typically processed at a temperature of from about 130 캜 to about 410 캜.

The reciprocating screw 22 preferably comprises one or more gates 30 that pressurize the molten thermoplastic material 24 toward the nozzle 26 and direct the flow of molten thermoplastic material 24 into the mold cavity 32, Forms a shot of the thermoplastic material to be injected into the mold cavity 32 of the mold 28 through no more than three gates. In another embodiment, the nozzles 26 may be separated from the one or more gates 30 by a supply system (not shown). The mold cavity 32 is formed between the first mold side portion 25 and the second mold side portion 27 of the mold 28 and the first and second mold side portions 25 and 27 are pressed or clamped by the clamping unit 34 Lt; / RTI > under pressure. The press or clamping unit 34 applies a clamping force greater than the force exerted by the injection pressure acting to separate the two mold halves 25 and 27 during the molding process so that the molten thermoplastic material (25, 27) while being injected into the first mold side (32). To support this clamping force, the clamping system 14 may include a mold frame and a mold base.

Once the shot of the molten thermoplastic material 24 is injected into the mold cavity 32, the reciprocating screw 22 stops moving forward. The molten thermoplastic material 24 takes the form of a mold cavity 32 and the melted thermoplastic material 24 is cooled inside the mold 28 until the thermoplastic material 24 is solidified. Once the thermoplastic material 24 is solidified, the press 34 releases the first and second mold side portions 25 and 27 and the first and second mold side portions 25 and 27 are separated from each other, The part can be discharged from the mold 28. The mold 28 may include a plurality of mold cavities 32 to increase the overall production rate. The shapes of the cavities in the plurality of mold cavities may be the same, similar, or different from each other. (The latter can be regarded as a group of mold cavities).

The controller 50 is provided with a nozzle sensor 52 located near the nozzle 26, a flow front end sensor 53 located within the mold cavity 32 or proximate the mold cavity 32, proximity to the reciprocating screw 22, A linear transducer 57, and a screw control 36, which are located in the housing. The controller 50 may include a microprocessor, memory, and one or more communication links. The flow front end sensor 53 may provide an indication of the position of the flow front end of the molten plastic material flowing through the mold cavity 32. Although the flow front end sensor 53 is illustrated as being close to the end of the mold cavity 32 in FIG. 1 (e.g., the position in the mold cavity that is the last time to fill the molten plastic material) Can be located at any point in the mold cavity between the position of the mold cavity 32 and the gate, which is the last time to fill with the thermoplastic material. If the flow front end sensor 53 is not located close to the end of the mold cavity 32, a time correction factor is applied to approximate when the flow front of the molten plastic material reaches the end of the mold cavity 32 . Positioning the flow front sensor 53 within 30% from the end of the mold cavity 32, preferably within 20% from the end of the mold cavity 32, and more preferably within 10% from the end of the mold cavity Lt; / RTI >

The linear converter 57 can measure the linear movement amount of the reciprocating screw 22. The nozzle sensor 52 and the flow front end sensor 53 detect the presence of the thermoplastic material optically, pneumatically, electrically, ultrasonically, mechanically or otherwise by sensing changes due to arrival of the flow front of the thermoplastic material can do. Linear transducers can measure linear movement mechanically, optically, pneumatically, magnetically, electrically, or ultrasonically, or the linear transducer can use any other method of measuring linear motion. When the pressure or temperature of the thermoplastic material is measured by the nozzle sensor 52, the nozzle sensor 52 transmits a signal indicative of pressure or temperature to the controller 50 so that as the filling is completed, To provide a target pressure within cavity 32 (or within nozzle 26). These signals can generally be used to control the molding process so that the controller 50 adjusts material viscosity, mold temperature, variations in melt temperature, and other variations that affect the filling rate. This adjustment can be made immediately during the molding cycle, or correction can be made in subsequent cycles. Moreover, some signals may be averaged over a number of cycles and then used by the controller 50 to control the molding process. The controller 50 is connected to the nozzle sensor 52, the flow front end sensor 53, the screw control 36 and / or the linear transducer 56 via wired connections 54, 55, 56 and 59, respectively . In another embodiment, the controller 50 may be used to communicate with the sensors 52, 53, 57 and / or the screw control 36 or the injection molding machine 50, such as a wireless connection, mechanical connection, hydraulic connection, pneumatic connection, To the nozzle sensor 52 via any other type of wired or wireless communication connection known to those skilled in the art that will allow control signals to be sent to any other component of the screw controller 56 ), And to a linear converter (57).

In the embodiment of Figure 1, the nozzle sensor 52 is a pressure sensor that measures (directly or indirectly) the melt pressure of the molten thermoplastic material 24 near the nozzle 26. The nozzle sensor 52 generates an electrical signal to be transmitted to the controller 50. The controller 50 then commands the screw control 36 to advance the screw 22 at a rate that maintains the desired melt pressure of the molten thermoplastic material 24 in the nozzle 26. This is known as a pressure controlled process. The nozzle sensor 52 can also directly measure the melt pressure while the nozzle sensor 52 can also measure other characteristics of the molten thermoplastic material 24, such as temperature, viscosity, flow rate, etc., Pressure can be measured indirectly. Likewise, the nozzle sensor 52 need not be located directly in the nozzle 26, but rather the nozzle sensor 52 may be located at any location within the mold 28 or injection system 12, Lt; / RTI > If the nozzle sensor 52 is not located in the nozzle 26, an appropriate correction factor may be applied to the measured characteristic to calculate an estimate of the melt pressure in the nozzle 26. The nozzle sensor 52 need not be in direct contact with the injected fluid, but may alternatively be capable of dynamically coupling with the fluid to sense pressure and / or other fluid properties of the fluid. If the nozzle sensor 52 is not located in the nozzle 26, an appropriate correction factor may be applied to the measured characteristic to calculate the melt pressure in the nozzle 26. In another embodiment, the nozzle sensor 52 need not be disposed at a position that is fluidly connected to the nozzle. Rather, the nozzle sensor 52 is capable of measuring the clamping force generated by the clamping system 14 at the mold separation line between the first mold part 25 and the second mold part 27. In one aspect, the controller 50 may maintain pressure in accordance with an input from the nozzle sensor 52. Alternatively, the sensor can measure the power demand by the electrical press, which can be used to calculate an estimate of the pressure in the nozzle 26.

Although an active closed loop controller 50 is illustrated in FIG. 1, other pressure regulating devices may be used in place of the closed loop controller 50. For example, a pressure regulating valve (not shown) or a pressure relief valve (not shown) may be substituted for the controller 50 to regulate the melt pressure of the molten thermoplastic material 24. More specifically, the pressure regulating valve and the pressure relief valve can prevent overpressurization of the mold 28. Another alternative mechanism for preventing overpressurization of the mold 28 is an alarm that is activated when an overpressure condition is detected.

Referring now to FIG. 2, an exemplary molded part 100 is illustrated. The molded part 100 is a thin-walled part. The molded part is generally considered to be thin-walled when the length L of the flow channel divided by the thickness T of the flow channel is greater than 100 (i.e., L / T> 100) but less than 1000. In the case of a mold cavity with a more complex geometry, the L / T ratio is obtained by integrating the T dimension over the length of the mold cavity 32 from the gate 30 to the end of the mold cavity 32, Can be calculated by determining the longest flow length to the end of the mold cavity 32. The L / T ratio can then be determined by dividing the longest flow length by the average part thickness. When the mold cavity 32 has more than one gate 30, the L / T ratio is determined by integrating L and T for the portion of the mold cavity 32 filled by each individual gate, The total L / T ratio for the cavity is the highest L / T ratio calculated for any of the gates. In some injection molding industries, thin walled components can be defined as parts having an L / T greater than 100, or having a L / T greater than 200, but less than 1000. The length L of the flow channel is the longest flow length as measured from the gate 30 to the end 104 of the mold cavity. Thin-walled components are particularly prevalent in the consumer product industry.

High L / T ratio components are often found in molded parts having an average thickness of less than about 10 mm. In consumer products, products with high L / T ratios generally have an average thickness of less than about 5 mm. For example, automotive bumper panels with high L / T ratios generally have an average thickness of less than 10 mm, whereas high glass cups with high L / T ratios generally have an average thickness of less than about 5 mm, A container (e.g., a tub or vial) with a high L / T ratio generally has an average thickness of about 3 mm or less, and a bottle cap enclosure having a high L / T ratio Individual toothbrush bristles, generally having an average thickness of about 2 mm or less, and having a high L / T ratio, generally have an average thickness of about 1 mm or less. The low constant pressure injection molding processes and apparatus disclosed herein are particularly advantageous for components having a thickness of 5 mm or less, and the disclosed process and apparatus are more advantageous for thinner components.

Thin walled components with a high L / T ratio cause certain obstacles in injection molding. For example, the thinness of the flow channel tends to cool the molten thermoplastic material before the material reaches the flow channel end 104. When this happens, the thermoplastic material hardens and no longer flows, which results in incomplete parts. To overcome this problem, conventional injection molding machines typically require injection molding of a molten thermoplastic material at very high pressures of more than 15,000 psi (103 MPa) to allow the molten thermoplastic material to cool and harden To quickly charge the battery. This is one reason why manufacturers of thermoplastic materials teach injection at very high pressures. Another reason for the conventional injection molding machine to be injected at high pressure is the increased shear, which increases the flow characteristics, as discussed above. This very high injection pressure requires, among other things, the use of a material that is very hard to form the mold 28 and the feed system. Moreover, the thin-walled part is a living hinge, a filament, a closure, a dispenser, a spout, a bellows, and an actuator, which must be filled before the material becomes hardened. , Such as, for example, one or more special features 105, as shown in FIG.

When charging at a substantially constant pressure (during an injection molding cycle), it was generally thought that the filling rate would need to be reduced relative to the conventional filling method. This means that the polymer will contact the cooled molding surface for a longer period of time before the mold is fully charged. Thus, more heat would need to be removed before filling, which would be expected to cause the material to harden before the mold is filled. It has unexpectedly been found that during the injection molding cycle, the thermoplastic material will flow when subjected to substantially constant pressure conditions, although part of the mold cavity is below the non-flow temperature of the thermoplastic material. It will be generally appreciated by those skilled in the art that such conditions would cause the thermoplastic material to continue to flow and harden rather than fill the entire mold cavity, thereby blocking the mold cavity. Without wishing to be bound by theory, it is believed that a substantially constant pressure condition during an injection molding cycle of an embodiment of the disclosed method and apparatus will result in a dynamic flow condition across the entire mold cavity (i.e., a constantly moving melt tip) . There is no hedging in the flow of the molten thermoplastic material as the molten thermoplastic material flows to fill the mold cavity so that at least a portion of the mold cavity is less than the non-flow temperature of the thermoplastic material, There is no.

It is also believed that as a result of the dynamic flow conditions, the molten thermoplastic material is able to maintain a temperature higher than the non-flow temperature, despite suffering such temperature in the mold cavity, as a result of shear heating . It is also believed that the dynamic flow conditions interfere with the formation of the crystalline structure in the thermoplastic material when the thermoplastic material begins its hardening process. The crystal structure formation increases the viscosity of the thermoplastic material, which can interfere with the flow suitable for filling the cavity. The reduction in crystal structure formation and / or crystal structure size may allow a reduction in thermoplastic material viscosity when the thermoplastic material flows into the cavity and experiences a lower temperature of the mold below the non-flow temperature of the material.

The disclosed low constant pressure injection molding methods and systems can be used to detect changes in material viscosity, changes in material temperature, and / or other sensor characteristics (e.g., The nozzle sensor 52, the flow front end sensor 53, or the linear converter 57 shown in Fig. 1). Measurements from these sensors can be communicated to the controller 50 to allow the controller 50 to calibrate the process in real time so that the tip of the melt reaches the end of the mold cavity before flashing of the mold, It is possible to ensure that the melt tip pressure which may cause a peak is relaxed. Moreover, the controller 50 can use the sensor measurements to adjust the peak output and peak flow points in the process, thereby achieving consistent processing conditions. In addition to using the sensor measurements to fine-tune the process in real-time during the current injection cycle, the controller 50 may also adjust the process over time (e.g., over a plurality of injection cycles). In this way, the current injection cycle can be corrected based on measurements that are generated at a timely earlier point in time during one or more cycles. In one embodiment, the sensor measurements may be averaged over many cycles to achieve process consistency.

In various embodiments, the mold may include a cooling system that maintains the entire mold cavity at a temperature below the non-flow temperature. For example, the surfaces of the mold cavity in contact with the shot containing the molten thermoplastic material may be cooled to maintain a lower temperature. Any suitable cooling temperature may be used. For example, the mold may be maintained at substantially room temperature. The integration of such a cooling system can advantageously improve the speed at which the molded injection molded part is cooled and ready to be discharged from the mold.

Thermoplastic material:

A variety of thermoplastic materials may be used in the low constant pressure injection molding method and apparatus of the present invention. In one embodiment, the molten thermoplastic material is characterized by a melt flow index of from about 0.1 g / 10 min to about 500 g / 10 min, as measured by ASTM D1238 performed at a temperature of about 230 C with a weight of 2.16 kg As described above. For example, for polypropylene, the melt flow index may range from about 0.5 g / 10 min to about 200 g / 10 min. Other suitable melt flow indices may be from about 1 g / 10 min to about 400 g / 10 min, from about 10 g / 10 min to about 300 g / 10 min, from about 20 g / 10 min to about 30 g / 10 min About 100 g / 10 min, about 50 g / 10 min to about 75 g / 10 min, about 0.1 g / 10 min to about 1 g / 10 min, or about 1 g / 10 min to about 25 g / 10 min . The MFI of the material is selected based on the application and use of the molded article. For example, a thermoplastic material having an MFI of from 0.1 g / 10 min to about 5 g / 10 min may be suitable for use as a preform for Injection Stretch Blow Molding (ISBM) applications. A thermoplastic material having an MFI of from 5 g / 10 min to about 50 g / 10 min may be suitable for use as a cap and closure for packaging articles. A thermoplastic material having an MFI of from 50 g / 10 min to about 150 g / 10 min may be suitable for use in the manufacture of buckets or tubs. Thermoplastic materials with an MFI of from 150 g / 10 min to about 500 g / 10 min may be suitable for molded articles having extremely high L / T ratios such as thin plates. Manufacturers of such thermoplastic materials generally teach that the material should be injection molded using melt pressures exceeding 41 MPa (6000 psi) and often significantly above 41 MPa (6000 psi). In contrast to the conventional teachings of injection molding such thermoplastic materials, embodiments of the low constant pressure injection molding method and apparatus of the present invention advantageously use such thermoplastic materials and are capable of less than 15,000 psi (103 MPa) Lt; RTI ID = 0.0 > MPa < / RTI > (15,000 psi) to form high quality injection molded parts.

The thermoplastic material may be, for example, a polyolefin. Exemplary polyolefins include, but are not limited to, polypropylene, polyethylene, polymethylpentene, and polybutene-1. Any of the aforementioned polyolefins may be supplied from a bio-based feedstock, such as sugar cane or other crops, to produce bio-polypropylene or bio-polyethylene. The polyolefin advantageously exhibits shear thinning when in a molten state. Shear thinning is a reduction in viscosity when the fluid is placed under compressive stress. Shear thinning may advantageously allow the flow of thermoplastic material to be maintained throughout the injection molding process. Without wishing to be bound by theory, it is believed that the shear thinning properties of thermoplastic materials, and in particular polyolefins, reduce the variation in material viscosity when the material is processed at a constant pressure. As a result, embodiments of the method and apparatus of the present invention may be less sensitive to variations in thermoplastic materials, such as from processing conditions, as well as from colorants and other additives. This reduced sensitivity to batch-to-batch variation of the properties of the thermoplastic material also advantageously allows post-industrial and post-consumer recycled plastics to be used in embodiments of the method and apparatus of the present invention. To be machined. After industrial use, post-consumer recycled plastics are derived from the final product, which as a consumer article would have been discarded as a solid waste product when their life cycle has been completed or not. Such recycled plastics, and blends of thermoplastic materials, inherently have significant inter-batch variations in their material properties.

The thermoplastic material may also be, for example, a polyester. Exemplary polyesters include, but are not limited to, polyethylene terephthalate (PET). The PET polymer may be fed from a bio-based feedstock, such as sugarcane or other crops, to produce a partial or complete bio-PET polymer. Other suitable thermoplastic materials include copolymers of polypropylene and polyethylene and copolymers of thermoplastic elastomers, polyesters, polystyrenes, polycarbonates, poly (acrylonitrile-butadiene-styrene), poly (lactic acid), bio- Such as poly (ethylene furanate) polyhydroxyalkanoate, poly (ethylene furanoate), (considered as an alternative or direct drop-in replacement for PET), polyhydroxyalkanoate, poly Amides, polyacetals, ethylene-alpha olefin rubbers, and styrene-butadiene-styrene block copolymers. The thermoplastic material may also be a blend of a plurality of polymeric materials and non-polymeric materials. The thermoplastic material may be, for example, a blend of high, medium, and low molecular weight polymers to produce a multi-modal or bi-modal blend. The multi-mode material can be designed in such a way as to produce a thermoplastic material with good flow properties while having satisfactory chemical / physical properties. The thermoplastic material may also be a blend of polymers with one or more small molecule additives. The small molecule may be, for example, a siloxane, or other lubricating molecule, which improves the flowability of the polymeric material when added to the thermoplastic material.

Other additives include inorganic fillers such as calcium carbonate, calcium sulfate, talc, clay (e.g., nanoclay), aluminum hydroxide, CaSiO _3, fiber or glass, crystalline silica formed by microspheres (e. G., Quartz, Nova site , Cristobalite), magnesium hydroxide, mica, sodium sulfate, lithopone, magnesium carbonate, iron oxide; Or organic fillers such as rice husk, straw, hemp fiber, wood flour, or wood, bamboo or sorghum fibers.

Other suitable thermoplastic materials include, but are not limited to, non-limiting examples of polymers that are produced directly from renewable polymers such as organisms, such as polyhydroxyalkanoates (e.g., poly (beta -hydroxyalkanoate) (NODAX®), and bacterial celluloses derived from plants, crops and forests, and biomass, such as polysaccharides and derivatives thereof (eg, polysaccharides, Such as gum, cellulose, cellulose esters, chitin, chitosan, starch, chemically modified starch, particles of cellulose acetate, proteins (e.g., zein, whey, gluten, Collagen), lipids, lignin, and natural rubber; thermoplastic starches derived from starch or chemically modified starches and present polymers derived from naturally-supplied monomers and oils Body, for example, bio-and a polyethylene terephthalate-polyethylene, bio-polypropylene, poly trimethylene terephthalate, polylactic acid, nylon (NYLON) 11, an alkyd resin, succinic acid-based polyester, and bio.

Suitable thermoplastic materials may include blends or blends of different thermoplastic materials as in the examples cited above. In addition, the different materials may be materials derived from the original bio-derived or petroleum-derived materials, or a combination of recycling materials of bio-derived or petroleum-derived materials. One or more of the thermoplastic materials in the blend may be biodegradable. And, in the case of a non-blended thermoplastic material, the material may be biodegradable.

An exemplary thermoplastic resin is provided in the following table along with its recommended working pressure range:

While more than one embodiment involves filling a substantially entire mold cavity with a shot comprising a molten thermoplastic material while maintaining the melt pressure of the shot comprising the molten thermoplastic material at a substantially constant pressure during the injection molding cycle, Certain thermoplastic materials benefit from the present invention at different constant pressures. Specifically: PP, nylon, PC, PS, SAN, PE, TPE, PVDF, PTI, PBT, and PLA at substantially constant pressure of less than 10000 psi; ABS at a substantially constant pressure of less than 55 MPa (8000 psi); PET at a substantially constant pressure of less than 40 MPa (5800 psi); An acetal copolymer at a substantially constant pressure of less than 7000 psi; In addition, the use of a poly (ethylene glycol) at a substantially constant pressure of less than 6000 psi, or 55000 psi, or 8000 psi, or 48000 psi, or 41000 psi, Ethylene furanate) polyhydroxyalkanoate, polyethylene furanoate (also known as PEF).

As described in detail above, the disclosed low injection molding method and apparatus embodiments can achieve one or more advantages over conventional injection molding processes. For example, the embodiments provide a simplified mold structure that eliminates the need for a more cost effective and efficient process, a mold cavity pressure at atmospheric pressure, and therefore a pressurized means, eliminating the need to balance the pre-injection pressure and the thermoplastic material of the mold cavity Which is less susceptible to variations in temperature, viscosity, and other material properties of the thermoplastic material, the ability to use mold cavity materials that are more cost effective and easier to machine, lower hardness, higher thermal conductivity, Robust processing methods, and the ability to produce high quality injection molded parts at substantially constant pressure without premature curing of the thermoplastic material in the mold cavity and without heating or maintaining a constant temperature within the mold cavity.

Referring now to FIG. 3, a typical pressure-time curve for a conventional variable high pressure injection molding process is illustrated by dashed line 200. In contrast, the pressure-time curve for the disclosed low constant pressure injection molding machine is illustrated by solid line 210.

In the conventional case, the melt pressure is ramped up much above 103 MPa (15,000 psi) and then maintained at a relatively high pressure exceeding 103 MPa (15,000 psi) during the first period 220. The first period 220 is the charging time at which the molten plastic material flows into the mold cavity. Thereafter, the melt pressure is reduced and maintained at a lower, but still relatively high pressure, typically above 10,000 psi (69 MPa) during the second period 230. The second period 230 is the packing time at which the melt pressure is maintained to ensure that all gaps in the mold cavity are back filled. After the packing is completed, the pressure may optionally drop again during the third period 232, which is the cooling time. The mold cavities in conventional variable high pressure injection molding systems are packed from the end of the flow channel back toward the gate. The material in the mold typically hardens near the end of the cavity, and then the material of the fully stiffened region gradually moves toward the gate position or positions. As a result, the plastic near the end of the mold cavity is packed at a reduced pressure for a shorter period of time than the plastic material near the gate position or locations. The geometric shape of the part, such as the very thin cross-sectional area intermediate the gate and the end of the mold cavity, can also affect the level of packing pressure in the regions of the mold cavity. Inconsistent packing pressures can cause inconsistencies in the finished product as discussed above. Moreover, conventional plastic packing in various solidification stages leads to some non-ideal material properties such as molded-in stress, sink, and non-optimal optical properties.

On the other hand, a low constant pressure injection molding system injects the molten plastic material into the mold cavity during the filling period 240 at a substantially constant pressure. The injection pressure in the example of Figure 3 is less than 41 MPa (6,000 psi). However, other embodiments may use higher pressures. After the mold cavity is filled, the injection molding system of low constant pressure progressively reduces the pressure over the second period 242 as the molded part cools. By using a substantially constant pressure during the injection molding cycle, the molten thermoplastic material maintains a continuous melt flow front that advances from the gate through the flow channel toward the end of the flow channel. In other words, the molten thermoplastic material maintains movement throughout the mold cavity, which prevents it from hardening at an early point in time. Thus, the plastic material remains relatively uniform at any point along the flow channel, which results in a more uniform and consistent finished product. By filling the mold with a relatively uniform pressure, the finished molded part forms a crystalline structure that can have better mechanical and optical properties than conventionally molded parts. Furthermore, the molded part at a constant pressure exhibits properties different from the skin layer of a conventionally molded part. As a result, molded parts under constant pressure can have better optical properties than conventionally molded parts.

Referring now to FIG. 4, the various stages of charging are separated by a percentage of the total charge time. For example, in a conventional variable high pressure injection molding process, the filling period 220 forms about 10% of the total filling time, the packing period 230 forms about 50% of the total filling time, the cooling period 232, Is about 40% of the total charge time. On the other hand, in a low constant pressure injection molding process, the charge period 240 makes about 90% of the total charge time, while the cooling time 242 is only about 10% of the total charge time. A low constant pressure injection molding process requires less cooling time because the molten plastic material is cooled as it flows into the mold cavity. Thus, by the time the mold cavity is filled, the molten plastic material is significantly cooled, though not enough to harden in the central cross-section of the mold cavity, and the total heat removed to complete the set-up process is small. Furthermore, since the molten plastic material remains in a liquid state throughout the fill and the packing pressure is transmitted through this molten central cross-section, the molten plastic material is in contact with the mold cavity wall (as opposed to hardening and shrinking) Maintain contact. As a result, the low constant pressure injection molding process described herein can fill and cool molded parts for less total time in conventional injection molding processes.

In the disclosed low constant pressure injection molding method and apparatus for molding high L / T parts, the part is injected into the mold cavity at an increased flow rate of the molten thermoplastic polymer to achieve the desired injection pressure, To maintain a substantially constant injection pressure. Low constant pressure injection molding methods and apparatus are particularly advantageous when molding thin wall components (e.g., parts having an L / T ratio greater than 100 and less than 1000) and using a shot size of from about 0.1 g to about 100 g. It is particularly advantageous that the maximum flow rate occurs within the first 30% of the cavity charge, preferably within the first 20% of the cavity charge, and even more preferably within the first 10% of the cavity charge. By adjusting the fill pressure profile, the maximum flow rate will occur within this preferred range of cavity filling and the shaped part will have at least some of the physical advantages (e.g., excellent strength, excellent optical characteristics, etc.) described above, This is because the crystal structure of the molded part is different from the conventional molded part. Moreover, since products with high L / T are thinner, these products require fewer pigments to impart the desired color to the resulting product. Moreover, in no-eye parts, the part will have less visual malformations due to more consistent molding conditions. Reducing the use of less or no pigments saves money.

Alternatively, the peak output can be adjusted to maintain a substantially constant injection pressure. More specifically, the filling pressure profile allows the peak output to occur within the first 30% of the cavity charge, preferably within the first 20% of the cavity charge, and even more preferably within the first 10% of the cavity charge Lt; / RTI > Adjusting the process so that the peak output occurs within a desired range and then has a decreasing output throughout the rest of the cavity charge produces the same gain for the shaped part described above with respect to the adjustment of the peak flow rate. Moreover, adjusting the process in the manner described above is particularly advantageous for thin wall components (e.g., L / T ratios of greater than 100 to less than 1000 and shot sizes from 0.1 g to 100 g).

Referring now to Figures 5A-5D and 6A-6D, a portion of the mold cavity (Figures 5A-5D) when being filled by a conventional injection molding machine, and a portion A portion of the mold cavity (Figs. 6A to 6D) is illustrated.

As illustrated in Figures 5A-5D, as a conventional injection molding machine begins to inject molten thermoplastic material 24 through the gate 30 into the mold cavity 32, a high injection pressure is applied to the molten thermoplastic material 24 Which tends to inject the molten thermoplastic material 24 into the mold cavity 32 at high speed which causes the molten thermoplastic material 24 to flow into a laminate 31 most commonly referred to as laminar flow 5a). These outermost laminations 31 are attached to the walls of the mold cavities and then cooled and hardened to form a hardened boundary layer 33 (Fig. 5B) before the mold cavity 32 is fully filled. However, as the thermoplastic material hardens, it also contracts away from the wall of the mold cavity 32, leaving a gap 35 between the mold cavity wall and the boundary layer 33. This gap 35 reduces the cooling efficiency of the mold. The molten thermoplastic material 24 also begins to cool and harden near the gate 30, which reduces the effective cross-sectional area of the gate 30. To maintain a constant volumetric flow rate, conventional injection molding machines must increase the pressure to pressurize the molten thermoplastic material through the narrowing gate 30. As the thermoplastic material 24 continues to flow into the mold cavity 32, the boundary layer 33 thickens (Fig. 5C). Ultimately, the entire mold cavity 32 is substantially filled with a hardened thermoplastic material (Fig. 5D). At this point, the conventional injection molding machine must retract the boundary layer 33 again against the wall of the mold cavity 32 to maintain the packing pressure to increase the cooling.

On the other hand, an injection molding machine with a low constant pressure causes the molten thermoplastic material to flow into the mold cavity 32 with a constantly moving flow front end 37 (Figs. 6A-6D). The thermoplastic material 24 behind the flow front end 37 remains molten until the mold cavity 37 is substantially filled (i.e., filled to over 99%) before it solidifies. As a result, there is no reduction in the effective cross-sectional area of the gate 30, which can be 70% to 100%, preferably 80% to 90% of the nominal wall thickness of the molded part. Moreover, since the thermoplastic material 24 is in a molten state behind the flow front end 37, the thermoplastic material 24 remains in contact with the walls of the mold cavity 32. As a result, the thermoplastic material 24 is cooling (without solidification) during the filling portion of the molding process. Thus, the cooled portion of the injection molding process of the disclosed low constant pressure need not be as long as the conventional process.

Because the thermoplastic material remains molten and continues to move into the mold cavity 32, less injection pressure is required than with conventional molds. In one embodiment, the injection pressure may be up to 6,000 psi (41 MPa). As a result, the injection system and the clamping system need not have a large output. For example, the disclosed low constant pressure injection molding apparatus can use a clamp requiring lower clamping force, and a corresponding lower clamping power source. The disclosed low constant pressure injection molding machine also employs electrical presses which are generally not sufficiently powerful for use in conventional grade 101 and 102 injection molding machines for molding thin wall components at variable high pressures due to their lower power requirements . Even when the electrical press is sufficient for use in some simple molds with fewer mold cavities, this process can be improved with the injection molding method and apparatus of the low constant pressure disclosed since smaller, less expensive electric motors can be used. The disclosed low constant pressure injection molding machine is used in the following types of electric presses: direct servo drive motor presses, double motor belt drive presses, dual motor planetary gear presses, and dual motor ball drive presses with rated power below 200 HP And may include one or more.

Referring now to FIG. 7, the operation of an exemplary molding cycle 1000 for an injection molding process at a low constant pressure is illustrated. The molding cycle 1000 can be performed on an injection molding machine of low constant pressure constructed according to the present invention, for example on the low constant pressure injection molding machine of FIG. More specifically, an exemplary molding cycle 1000 is performed with a mold including a first mold side and a second mold side (at least one of the first mold side and the second mold side has a density of 30 BTU / Having an average thermal conductivity of less than or equal to 223 BTU / HRF < 0 > F), and a low constant pressure injection molding machine having a mold cavity formed between the first mold side and the second mold side . In some preferred embodiments, both the first and second mold sides have an average thermal conductivity of less than or equal to 223 BTU / HR FT < 0 > F and less than or equal to 30.9 BTU / Lt; / RTI >

Some preferred materials for making the first and / or second mold sides are aluminum (e.g., 2024 aluminum, 2090 aluminum, 2124 aluminum, 2195 aluminum, 2219 aluminum, 2324 aluminum, 2618 aluminum, 5052 aluminum, 5059 aluminum, Aircraft grade aluminum, 6000 series aluminum, 6013 aluminum, 6056 aluminum, 6061 aluminum, 6063 aluminum, 7000 series aluminum, 7050 aluminum, 7055 aluminum, 7068 aluminum, 7075 aluminum, 7076 aluminum, 7150 aluminum, 7475 aluminum, QC-10, Alumold ^TM , Hokotol ^TM , Duramold 2 ^TM , Duraform 5 ^TM , and Alumec 99 ^TM ), BeCu (e.g., C17200, C18000, C61900, C62500 (For example, beryllium, bismuth, chromium, copper, gallium, iron, cobalt, and the like), C64700, C82500, Moldmax LH ^TM , Moldmax HH ^TM , and Protherm ^TM ) Lead, Magnet , Manganese, include silicon, titanium, vanadium, zinc, and zirconium), any alloy of copper (e. G., Magnesium, zinc, nickel, silicon, chromium, aluminum, bronze). These materials may have a Rockwell C (Rc) hardness of 0.5 Rc to 20 Rc, preferably 2 Rc to 20 Rc, more preferably 3 Rc to 15 Rc, and more preferably 4 Rc to 10 Rc. Although these materials may be more ductile than tool steel, the thermal conductivity characteristics are more desirable. The disclosed low constant pressure injection molding methods and apparatus advantageously allow molds made of such smoother, higher thermal conductivity materials to have molds of over one million cycles, preferably from one and a half million cycles, and more preferably 200 And operate under molding conditions that allow it to obtain a lifetime of from full cycle to 5 million cycles.

Initially, at 1110, the molten thermoplastic material is advanced into a mold cavity defining a thin walled component (e.g., 100 < L / T < 1000). The shot of the molten thermoplastic material may be from 0.5 g to 100 g and may be advanced into the mold cavity through no more than three gates. In some cases, one or more of the three or fewer gates may be 70% to 100% of the nominal wall thickness of the part of which the cross-sectional area is formed in the mold cavity, and preferably 80% to 90% of the nominal wall thickness. In some instances, this percentage may correspond to a gate size of 0.5 mm to 10 mm.

At 1112, the molten thermoplastic material is advanced into the mold cavity until the mold cavity is substantially filled. The mold cavity can be substantially filled when the mold cavity is filled by more than 90%, preferably by more than 95%, and more preferably by more than 99%. After the mold cavity is substantially filled, at 1114, the molten thermoplastic material is cooled until the molten thermoplastic material is substantially solidified or solidified. The molten thermoplastic material may be actively cooled by a cooling liquid flowing through at least one of the first and second mold sides, or may be passively cooled through conduction and convection into the atmosphere.

After the thermoplastic material has cooled, at 1116, the first and second mold sides can be separated to expose the cooled thermoplastic material. At 1118, the cooled thermoplastic material (in the form of molded parts) can be removed from the mold. The thermoplastic material can be, for example, discharged, dumped, extracted (via a manual or automated process), pulled, pushed, gravitated, or cooled thermoplastic from the first and second mold sides Can be removed by any other means of separating the material.

After the cooled thermoplastic material is removed from the first and second mold sides, at 1120, the first and second mold sides may be closed to re-mold the mold cavity, which may be used to accommodate a new shot of molten thermoplastic material The first and second mold sides are prepared, thereby completing a single molding cycle. The cycle time 1001 is defined as a single iteration of the molding cycle 1000. A single molding cycle may take from 2 seconds to 15 seconds, preferably from 8 seconds to 10 seconds, depending on the part size and material.

All injection molding processes are sensitive to changes in viscosity of the molten plastic material. A change in the viscosity of the molten plastic material can cause defects in the molded part, such as insufficient material (e.g., short shot), and flashing. Any number of factors may cause the viscosity of the molten plastic material to vary. For example, changes in ambient temperature or pressure, the addition of a colorant, changes in shear conditions between the feed system and the last cavity location filled with molten plastic material (otherwise known as "end of fill location"), Both of the viscosity change of the plastic material itself and the change of other conditions may cause the viscosity of the molten plastic material to change. As the viscosity of the molten plastic material changes, the pressure required to press the molten plastic into the mold will also change. For example, as the viscosity increases, the pressure required to press the polymer into the mold cavity will increase because the polymer is thicker and more difficult to move into the mold cavity. On the other hand, if the viscosity is reduced, the pressure required to press the polymer into the mold cavity will decrease because the polymer is thinner and more likely to migrate into the mold cavity. If no adjustment is made to the injection pressure or cycle time, the molded part may have defects. Current injection molding machines and injection molding processes have a time-based molding cycle. In other words, since the injection molding cycle ends at a predetermined time, the molding cycle is controlled by time among other factors. As a result, a change in viscosity for the molten plastic material can cause the molten plastic material to reach the end of the mold cavity at a time different from the predetermined time.

Referring now to FIG. 8, a pressure versus time graph is illustrated for a single injection molding cycle. During the initial stage of the injection molding cycle, the pressure rapidly increases to a predetermined target value 1210 (e.g., "fill pressure"), where pressure is maintained as the mold cavity is filled. At a first time t _t (or _transducer ) 1212, as the molten plastic material is near the end of the mold cavity 32, as represented by the flow front end sensor 53 (Fig. 1) As the material in the mold cavity 32 cools, the pressure is reduced from 1214 to a lower pressure (e.g., "pack and holding pressure"). The molded part is discharged from the mold cavity 32 at a second time t _s (or t _step ) 1216, which is the total cycle time from the start of the charge sequence to the end of the charge cycle in which the mold is open.

The change in viscosity of the molten plastic material may affect the time at which the molten plastic material reaches the end of the mold cavity 32 at t _s or the end of the fill location in the mold cavity. For example, if the viscosity of the molten plastic material increases (with the possibility of a "shot shot"), the molten plastic material may be heated to a filling pressure for a longer period of time, as exemplified by broken line 1220a Can be maintained. In this example, the flow front end sensor 53 can detect the molten plastic material at a later time than the predetermined time. The predetermined time at which the molten plastic reaches the flow front sensor can be calculated or experimentally derived for the ideal conditions and constant viscosity for the molten plastic material. On the other hand, if the viscosity of the molten plastic material decreases (with the possibility of "flashing"), the molten plastic material is maintained at the fill pressure for a shorter period of time, as exemplified by broken line 1220b . In this example, the flow front end sensor 53 can detect the molten plastic material at a time (t _t ) earlier than a predetermined time.

In the case of a pressure-controlled filling process, an optimal filling pressure profile can be determined experimentally. This optimal pressure profile establishes the optimal plastic pressure for the nominal polymer at each instant of the charge cycle. The polymer pressure is sensed at a location within the polymer flow channel prior to the mold cavity. In one example, the polymer pressure can be sensed by the nozzle sensor 52. However, the polymer pressure can be sensed at any location on the upstream side of the gate. The nominal flow rate can be assigned at each instant during the charge cycle by calculating or directly measuring the polymer flow rate during the charge cycle. In addition, the force required to move a given volume of polymer through the supply system and into the mold cavity can be determined for the optimal filling pressure profile through experiments or calculations.

For each charge cycle, the controller 50 compares the nominal (or optimal) force required to move the polymer through the system and the actual force required to move a given volume of polymer through the supply system during the charge cycle . If the actual force is higher than the nominal force, material flowability increases. As a result, a corresponding and proportional increase in the charging force is required to produce an optimal polymer flow profile.

At any given point in the system, the polymer pressure is an indication of the magnitude of the force required to move the polymer through the system. Additionally, at any given point in the system, the polymer pressure is directly proportional to the magnitude of the force required to move the polymer through the system. As a result, the polymer pressure can be used to balance or offset the contractile force in the polymer when the polymer is cooled in the mold cavity.

In the case of a hydraulic injection press, a proportional valve may be used to control the flow of hydraulic fluid to the system acting on the injection screw 22. An electronic control signal may be transmitted to the proportional valve, which causes the proportional valve to move in response to the control signal. When the voltage of the control signal to the proportional valve increases, the proportional valve moves to deliver more hydraulic pressure to the reciprocating screw 22, thereby pushing more of the polymer through the supply system. As discussed above, as the polymer viscosity changes, the resistance to flow through the system will vary. Thus, in order to maintain the polymer flow rate through the feed system at a flow rate equivalent to that for the nominal fluid viscosity material, the voltage of the control signal to the proportional valve must be varied. This same relationship can be established for the electric press, where the voltage of the control signal changes the number of amps to the servomotor. Alternatively, in the case of separate but synchronized electro-hydraulic hybrid injection presses, a control signal is transmitted to the electric servo drive and to the proportional valve.

Referring now to FIG. 9A, graph 1310 illustrates a control signal response (voltage unit) from the controller to the proportional valve over time. The vertical axis 1312 of the graph corresponds to the control signal voltage in milliamperes, and the horizontal axis 1314 of the graph corresponds to the time in milliseconds. The ratio of the change in the voltage of the control signal to the proportional valve to the time period for such change can be used to control the injection process. This value can be expressed, for example, as a ratio of millivolts per time, and is defined herein as a flow coefficient (FF). The flow coefficient ratio may be determined for the injection molding process for any molding machine, including hydraulic, electric, or any other molding machine. The flow coefficient FF can be mathematically expressed by the following equation:

FF = (CS1 - CS2) T;

Where CS1 and CS2 are control signals (e.g., can be measured in millivolts) measured at different moments in time during the injection molding cycle.

The control signal from the controller 50 to the proportional valve is a continuous signal as illustrated in FIG. 9A, although the "first control signal" and the "second control signal" are referred to herein. However, this control signal may also be used to determine the first and second control signals at a time instant (e.g., at a first time tl 1316 and a second time t2 1318) during an injection molding cycle . The voltages measured at these temporally distinct moments are referred to herein as the first control signal voltage 1320 and the second control signal voltage 1322, respectively. Although the control signal in the described embodiment is at least partly defined by the voltage, other control signal parameters may similarly be used. For example, if the control signal is essentially pneumatic, the flow coefficient may be defined by the control signal parameter of the pressure. Similarly, if the control signal is intrinsically optical, the flow coefficient can be defined by control signal parameters of brightness or intensity. Those skilled in the art will be able to select appropriate control signal parameters in view of the nature of the control signal itself.

The preferred time increments for t1 and t2 are from 0.1 millisecond to 10 milliseconds, preferably 0.5 milliseconds to 5 milliseconds, more preferably 0.75 milliseconds to 2 milliseconds, and even more preferably, about 1 millisecond . A period within the disclosed range provides a very immediately responsive control system that quickly adjusts the control signal in response to changes in fluidity.

In the case of a pressure-controlled process, such as the pressure controlled process described herein, the controller 50 can adjust the flow of polymeric material to reach a predetermined pressure set point. As the flow decreases, and as the flow along the length corresponding to the resistance is reduced, and require more flow to reach the pressure set point, so that the actual FF _l may be higher than the expected or optimal FF. This relationship can be used to detect whether the system fluidity has changed at any time during the injection molding cycle, instantaneously or periodically. Such system fluidity changes can be caused by any number of factors, including changes in molecular weight distribution in the polymer, and shear or temperature changes. For example, if the actual FF is higher than the optimal FF, the flowability decreases. Similarly, if the actual FF is lower than the optimal FF, the flowability increases. This change in FF is caused by the system attempting to maintain a predetermined pressure. If the fluidity is low, the proportional valve should release additional hydraulic pressure to the system in order for the higher viscosity material to reach the predetermined pressure set point. Likewise, if the fluidity is increased, the proportional valve should release less hydraulic pressure into the system to make the lower viscosity material reach the predetermined pressure set point. The control response to increase or decrease the polymer pressure may be linear or nonlinear, and may be based on dependent or independent system variables.

In addition, the difference between the actual FF and the optimum FF can be adjusted to the nominal viscosity of the polymer so that the change in the control signal is adjusted to the corresponding change in flowability of the molten plastic material as measured in real time . Thus, this difference between the actual FF and the optimal FF can be exponentiated with respect to the flowability.

The actual FF can be compared to the optimal FF at any point in the process and the difference can be used to adjust the target fill pressure for the remainder of the charge cycle. For example, if the FF is compared early (e.g., the first 10% of the cycle) during the cycle, the target pressure for the remainder of the cycle (e.g., the last 90% Or downward. Furthermore, the comparison between the actual FF and the optimum FF can be used to adjust the target pressure of the subsequent injection cycle, even if adjustment to the target pressure within the current injection cycle is made. By comparing the actual FF with the optimal FF, the target filling pressure can be adjusted within a cycle or between cycles to account for changes in polymer fluidity.

In some cases, the difference between the first control signal and the second control signal can be used to determine the incremental (e.g., as measured by linear converter 57 and the volume of material flow per unit of movement) As a ratio to the movement, the containing factor can be defined. Such factors are also defined herein as viscosity change index (VCI). VCI takes into account the effect of changes in system pressure (P), polymer volume (V), system temperature (T), and material composition or molecular weight distribution (C). VCI is a function of the sum of the effects of P, V, T, and C in the entire polymer flow system and is expressed by the following equation:

VCI = f [? P,? V,? T,? C].

Alternatively, it is expressed as the following measured variable:

VCI = (CS1-CS2) / S;

Where CS1 is the first control signal, CS2 is the second control signal, and S is the positional difference relative to the melt transfer machine component, such as the injection screw 22.

The VCI can be used to achieve an optimal polymer flow profile by enabling the instant control of the filling process by controlling the process to compensate for changes in flow properties of the molten plastic material during the injection molding cycle of the injection molding system have. Similar to the FFs described above, the change in VCI represents a change in fluidity, as measured in real time, at any time during the charge cycle, and can then be used to increase or decrease the fill pressure in response to that change have.

Referring now to FIG. 9B, graph 1350 illustrates a control signal response (voltage unit) from the controller to the proportional valve over time. The vertical axis 1352 of the graph corresponds to the control signal voltage in milliamperes and the horizontal axis 1354 of the graph corresponds to the distance travel of the melt transfer machine component in microns.

The control signal can be measured at different instants in time during the injection molding cycle (e.g., the first time t1 1356 and the second time t2 1358). The voltages measured at these temporally distinct moments are referred to herein as the first control signal voltage 1360 and the second control signal voltage 1362, respectively. Although the control signal in the described embodiment is at least partly defined by the voltage, other control signal parameters may similarly be used. For example, if the control signal is essentially pneumatic, the flow coefficient may be defined by the control signal parameter of the pressure. Similarly, if the control signal is intrinsically optical, the flow coefficient may be defined by a control signal parameter of brightness or intensity. Those skilled in the art will be able to select appropriate control signal parameters in view of the nature of the control signal itself.

The VCI serves as a "soft sensor" in the system because it calculates values corresponding to changes in polymer viscosity using other sensors and measured variables. FF can also be used as a "soft sensor" in the system. VCI "soft sensors" can be used to determine the change in material fluidity during a charge cycle and thus to allow immediate control over the filling process to achieve an optimal polymer flow profile. The change in VCI may indicate a change in the flowability of the molten plastic material at any time during the charge cycle, and this value can then be used to control the fill pressure. The VCI can be determined at a plurality of instantaneous points during the charge cycle by comparing the ratio of the difference between CV1 and CV2, as compared to a 1 micron movement of the injection unit. If the VCI is increased, a corresponding control response is made to increase the target filling pressure for the next increment of charge to compensate for the change in fluidity. If the VCI decreases, a corresponding control response is made to reduce the target filling pressure for the next increment of charge. The control response can be linear or nonlinear, and can be adjusted based on dependent or independent system variables.

For the purpose of controlling the injection molding process, it is possible to calculate the VCI at any time during the injection molding cycle and then use the VCI as the basis for a single adjustment to the target filling pressure for subsequent portions of the injection molding cycle. If the VCI is calculated early (e.g., the first 10% of the cycle) during the injection molding cycle, the target filling pressure for the remainder of the injection molding cycle (e.g., the remaining 90% of the cycle) may be adjusted upwards or downwards . Alternatively, the VCI calculation can be used to adjust the subsequent injection molding cycle, even if the target pressure of the current injection molding cycle is not adjusted. By calculating the VCI, a control response can be made to increase or decrease the charge pressure in real time. By calculating the VCI (or FF) in real time, the disclosed system and method advantageously responds almost immediately to changes in system fluidity, and can also be used to compensate for any fluidity change for the current injection cycle as well as for subsequent injection cycles Quickly adjust process variables. The disclosed soft sensor may be included in the control logic that determines the correction input based on the rate of change of the soft sensor or the difference between the soft sensor value and the reference curve or data table.

The injection pressure can also be continuously adjusted throughout the injection molding cycle. For example, if the VCI is calculated at any point in the injection molding cycle, then the VCI can be fed forward and adjustment to the target filling pressure can be made for the next increment of the injection molding cycle. For example, the VCI may be calculated every 0.5 milliseconds, and the subsequent target filling pressure may be adjusted based on the immediately preceding VCI (or the average of one or more previous VCIs). This process can be repeated throughout the injection molding cycle to control the process on a closed loop basis throughout the injection molding cycle. When calculating the VCI, a control response can be made to increase or decrease the charge pressure.

Individual press specifications such as proportional valve design, servo motor output, barrel diameter, hydraulic capacity, check ring performance, and other press variables are considered in the calculation of control variables by using the ratio or by using dimensionless coefficients .

The fluidity of the polymeric material may vary during the injection molding process for several reasons. The nominal viscosity of the polymer may vary slightly from batch to batch due to inconsistent manufacturing or poor quality control. When operating a molding operation, these viscosity changes cause a change in the pressure required to fill the mold cavity. These viscosity changes can cause quality problems, and reduced productivity. For example, if the viscosity increases significantly, the injection molding system does not produce the proper force to push the polymer into the mold and can cause a "short shot ". In addition, if the short shot area prevents proper ejection of the component from the mold, the component can be trapped within the mold and the captured component can damage the mold at the time of closure of the mold with preparation of the next shot of the polymer. This is particularly of concern in the case of soft metallurgical molds such as aluminum where the material is more easily deformed than a harder material such as a hardened tool steel. If the polymer viscosity is significantly reduced, too much pressure may be applied to fill the mold and result in "flashing" the mold. If flashing occurs, the parting line edge may be damaged as the material is pressed between the shut-off surfaces. Flashing is particularly concerned in the case of soft metallurgical molds such as aluminum where the material is more easily deformed than harder materials such as hardened tool steel.

In the case of recycled polymers, the feedstock is highly variable, due to the multiple material sources that are blended together to form a batch of recycled resin. The regenerator attempts to blend many different melt flow index (MFI) resins together to achieve the target average MFI. However, the material comprising the blend is highly variable, and thus the resulting blend may range in the + or - 10 MFI, or even more, than that. For the processor, this creates a difficult processing scenario, since the MFI variation causes a constant change in processing conditions. In such cases, the machine operator should regularly monitor the process and any parts produced and regularly calibrate the process to avoid producing waste parts or damaging the molds.

The addition of the colorant masterbatch may also cause a change in the viscosity of the polymer. These viscosity variations require the molding machine operator to make process adjustments to account for these variations. In addition, the master batch is typically concentrated and added to a relatively low level, which is in the range of about 0.5 to about 10% of the total material composition. Small variations in the addition of intrinsic, masterbatches in the metering method of further masterbatching can cause large variations in the viscosity of the polymer. As a result, the operator must be mindful of the molding machine in order to make the necessary adjustments to avoid producing waste parts or damaging the mold.

The viscosity is also temperature dependent. In a molding operation, the temperature of the water cooling the molding system may vary. For example, when using a water tower to cool a mold, the temperature of the water will be higher on a warmer day, especially after continued warm weather, and colder at night or during longer cooler weather. These temperature variations can cause the viscosity of the material in the forming system to vary. As a result, part quality changes and creates the possibility of damage to the waste and mold. Other sources of temperature fluctuations may include temperature fluctuations at the nozzles or in heater bands that maintain the temperature rise in the supply system. Molding equipment operators must continually monitor and control these temperature fluctuations.

To solve the problem caused by the change in fluidity, the controller 50 (Fig. 1) controls the screw control 26 (Fig. 1) to maintain the target injection pressure, Thereby increasing or decreasing the movement of the endoscope.

Referring now to FIG. 10, a logic diagram 1400 of a process for considering a change in viscosity is illustrated. An injection molding controller is provided at 1410 having at least one mold cavity and a pressure control output configured to provide a control signal to at least partially determine an injection molding pressure for the injection molding process of the injection molding machine, / RTI &gt; At 1430, a first control signal is measured at a first time during the injection molding cycle. At 1440, a second control signal is measured at a second time during the injection molding cycle, following the first time. At 1450, the first control signal from the pressure control output and the second control signal from the pressure control output are compared. At 1460, a third control signal for the pressure control output is determined at a third time following the second time, the third control signal being based at least in part on the comparison result.

FIG. 11 illustrates one embodiment of a closed loop control system that may be used to perform the method illustrated in FIG. The control system 1700 illustrated in FIG. 11 may be used to implement and improve the injection molding process illustrated in FIG. 10 for a particular component or material by using any one or more of the process variables generally represented by reference numeral 1710 And provides an open architecture for These process variables 1710 represent physical values obtained from various sensors in an injection molding machine. These physical values are processed by the controller 50. The processing may include any number of calculations, such as those indicated by reference numeral 1712. These calculations can be used for transforms or scaling to reflect the importance of certain variables through weights. Such calculations may include rule-based algorithms, heuristic algorithms, genetic algorithms, or other calculations, such as those described above with respect to flow coefficients and viscosity indexes.

The process variable 1710 can be used directly to determine the control variable 1716, such as a control signal, and only to the core variable 1714, with or without scaling, or via the variable calculation 1712. For example, the variable calculation 1712 may include the VCI or flow coefficient calculation 1713 described above. The control variable 1716 represents the feedback signal for the PID control loop 1718. Although any number of desired setpoints, represented generally by reference numeral 1720, may be used as input to the PID control loop 1718, the systems and methods described herein, which are pressure controlled injection molding processes, Change 1722 is used as the control input. As a result, the PID control loop 1718 continuously considers the change in flowability of the molten plastic material by continuously controlling the control signal transmitted to the proportional valve 1724.

In some cases, the injection molding machine may include an electrical press, and the controller may change the electronic control signal to the servo motor of the electrical press.

As discussed above, the change in viscosity of the molten plastic material can be caused by any number of factors. For example, an operator may want to reuse parts of poor quality by re-grinding parts of poor quality and mixing the re-ground plastic material with the original plastic material. The mixing of the re-ground plastic material with the original plastic material will change the MFI of the combined material. Similarly, the operator may wish to change the color of the part during injection operation by introducing the colorant into the molten plastic material. The introduction of the colorant will often change the MFI of the molten plastic material. Finally, a change in ambient operating conditions can also change the viscosity of the molten plastic material. For example, when the ambient temperature increases, the viscosity of the molten plastic material often increases. Likewise, when the ambient temperature decreases, the viscosity of the molten plastic material is often reduced.

The disclosed low constant pressure injection molding methods and machines advantageously reduce cycle times for the molding process while increasing component quality. Moreover, the disclosed low constant pressure injection molding machine can, in some embodiments, employ an electric press that is generally more energy efficient and requires less maintenance than a hydraulic press. In addition, the disclosed low constant pressure injection molding machine has the advantage that a more flexible support structure and a more adjustable delivery structure, such as a wider platen width, increased tie bar spacing, removal of the tie bar, A lighter weight configuration that facilitates the use of a non-naturally balanced supply system. Thus, the disclosed low constant pressure injection molding machine can be modified to meet delivery requirements and can be more easily customized for certain molded parts.

In addition, the disclosed low constant pressure injection molding machines and methods have the advantage that the molds can be made of a more flexible material (e.g., a thermoplastic material) having a higher thermal conductivity (e.g., a thermal conductivity of greater than about 20 BTU / HRFTF) A material having an Rc of less than about 30), leading to a mold with improved cooling capability and more uniform cooling. Because of the improved cooling capability, the injection molds of the disclosed low constant pressure may comprise a simplified cooling system. Generally speaking, the simplified cooling system includes fewer cooling channels, and the included cooling channels can be more straightforward, thus having fewer machining axes. An example of an injection mold with a simplified cooling system is disclosed in U.S. Patent Application No. 61 / 602,781, filed February 24, 2012, which is hereby incorporated by reference herein.

The lower injection pressure of an injection molding machine with a lower constant pressure is less than one million times that a mold made of such a softer material will not be possible in a conventional injection molding machine because these materials will be destroyed before a molding cycle of one million times in a high- Lt; / RTI &gt;

The terms "substantially "," about ", and "approximately" are used herein to refer to the degree of intrinsic uncertainty attributable to any quantitative comparison, value, measure, May be used. This term is also used herein to indicate the extent to which the quantitative expression can vary from the stated criteria, without causing a change in the basic function of the subject matter in question. The terms " substantially ", " about ", and "approximately" mean that a quantitative comparison, value, measure, or other expression may be within 20% of the stated criteria.

It will now be apparent that various embodiments of the products illustrated and described herein can be produced by a substantially constant low pressure molding process. Although specific reference may be made in this text to the product or consumer product product itself for inclusion in consumer products, the molding methods discussed herein may be used in connection with products intended for use in the consumer goods industry, the catering industry, the transportation industry, the medical industry, It will be apparent that the invention may be adapted for use. Moreover, those skilled in the art will appreciate that the teachings disclosed herein may be used in the construction of multiple material molds, stack molds, including rotating molds and core backing molds, in combination with mold decorations, insert molding, Will recognize.

Portions, or portions of any of the embodiments disclosed herein may be combined with portions, portions, or all of the other injection molding embodiments known in the art, including those described below.

An embodiment of the present invention is directed to an apparatus and method for injection molding at low constant pressure, which is disclosed in US 2012-0294963 A1, May, 2012, entitled " Apparatus and Method for Injection Molding at Low Constant Pressure & May be used in conjunction with an embodiment for injection molding at low constant pressure, as disclosed in U.S. Patent Application Serial No. 13 / 476,045, filed on September 21, 2001 (the applicant's case 12127) .

An embodiment of the present invention is described in U.S. Patent No. 8,757,999, entitled " Alternative Pressure Control for a Low Constant Pressure Injection Molding Apparatus & May be used in conjunction with an embodiment for pressure control, such as disclosed in U.S. Patent Application No. 13 / 476,047, filed May 21, 2001 (the applicant's case 12128), which is incorporated herein by reference.

An embodiment of the present invention is described in U. S. Pat. Nos. 5,192,125, entitled " Non-Naturally Balanced Feed System for an Injection Molding Apparatus " Can be used in conjunction with an embodiment for a non-natural flat feed system, such as that disclosed in U.S. Patent Application No. 13 / 476,073, filed on May 21 (Applicant's Case 12130) It is included as a reference.

An embodiment of the present invention is directed to a method for injection molding at low, substantially constant pressure, which is disclosed in US 2012-0295050 A1, May, 2012, entitled " Method for Injection Molding at Low, Substantially Constant Pressure & May be used in conjunction with an embodiment for injection molding at a low, substantially constant pressure, such as disclosed in U.S. Patent Application No. 13 / 476,197, filed on September 21, 2001 (the applicant's case 12131Q) &Lt; / RTI &gt;

An embodiment of the present invention is directed to a method for injection molding at a low, substantially constant pressure, which is disclosed in US 2012-0295049 A1, May, 2012, entitled " Method for Injection Molding at Low, Substantially Constant Pressure & May be used in conjunction with an embodiment for injection molding at a low, substantially constant pressure, as disclosed in U. S. Patent Application Serial No. 13 / 476,178, filed on December 21 (Applicant's case 12132Q) &Lt; / RTI &gt;

An embodiment of the present invention is described in U.S. Patent Application No. 13 / 774,692, filed February 22, 2013, entitled " High Thermal Conductivity Co-Injection Molding System " For example, as disclosed in Applicant's case 12361, which is incorporated herein by reference.

Embodiments of the present invention may be practiced in the name of the invention as "a simplified evaporation cooling system, or an injection mold having a simplified cooling system with a unique cooling fluid " (Simplified Cooling System with Exotic Cooling Fluids) With the embodiment for molding with a simplified cooling system, as disclosed in U.S. Patent No. 8,591,219, U.S. Patent Application No. 13 / 765,428, filed February 12, 2013 (the applicant's case 12453M) , Which is hereby incorporated by reference.

An embodiment of the present invention is directed to a method and apparatus for the injection molding of a substantially constant pressure of a thin wall component, as described in the " Method and Apparatus for Constant Pressure Injection Molding of Thinwall Parts & May be used in conjunction with an embodiment for molding a thin wall component, such as disclosed in the filed U.S. Patent Application No. 13 / 476,584 (Applicant's case 12487), which is incorporated herein by reference.

An embodiment of the present invention is described in U.S. Patent Application No. 13 / 672,246, filed November 8, 2012, entitled " Injection Mold With Fail Safe Mechanism " Can be used in conjunction with an embodiment for molding using a safety mechanism, such as disclosed in Applicant's case 12657, which is incorporated herein by reference.

An embodiment of the present invention is described in U.S. Patent Application No. 13 / 682,456, filed November 20, 2012, entitled " Method for Operating a High Productivity Injection Molding Machine " Can be used in conjunction with embodiments for high productivity molding, such as disclosed in U.S. Patent Application Serial No. 12673R (Applicant's case 12673R), which is incorporated herein by reference.

An embodiment of the present invention is directed to a method of forming a thermoplastic polymer and a hydrogenated castor oil, which process is described in U. S. Patent &lt; RTI ID = 0.0 &gt; Can be used in conjunction with embodiments for molding certain thermoplastic materials, such as disclosed in Application Serial No. 14 / 085,515 (Applicant's Case 12674M), which is incorporated herein by reference.

An embodiment of the present invention is described in U.S. Patent Application No. 14 / 085,515, filed November 21, 2013, entitled " Reduced Size Runner for an Injection Mold System " May be used in conjunction with an embodiment for a runner system, such as that disclosed in U. S. Patent Application Serial No. 12677M, which is hereby incorporated by reference.

An embodiment of the present invention is directed to an injection molding machine having a low constant pressure injection molding system with a variable position molding cavity, Can be used in conjunction with embodiments for a mobile molding system, such as disclosed in patent application No. 61 / 822,661 (Applicant's case 12896P), which is incorporated herein by reference.

Embodiments of the present invention are described in detail in "Injection Molding Machines and Methods for Accounting for Changes in Material Properties during Injection Molding Operation" , U.S. Patent Application No. 61 / 861,298, filed on August 20, 2013 (the applicant's case 13020P), which is incorporated herein by reference in its entirety, &Lt; / RTI &gt;

Embodiments of the present invention are described in detail in "Injection Molding Machines and Methods for Accounting for Changes in Material Properties during Injection Molding Operation" May be used in conjunction with an embodiment for an injection mold control system, such as disclosed in U.S. Patent Application No. 61 / 861,304, filed August 20, 2013 (Applicant's Case 13021P) &Lt; / RTI &gt;

Embodiments of the present invention are described in detail in "Injection Molding Machines and Methods for Accounting for Changes in Material Properties during Injection Molding Operation" , U.S. Patent Application No. 61 / 861,310, filed August 20, 2013 (Applicant's Case 13022P), which is incorporated herein by reference in its entirety, &Lt; / RTI &gt;

An embodiment of the present invention is directed to U.S. Patent Application No. 61 / 918,438, entitled " Methods of Forming Overmolded Articles, " filed December 19, 2013 Case 13190P), which is hereby incorporated by reference in its entirety, for use in conjunction with embodiments for molding overmolded articles using injection molding.

An embodiment of the present invention is directed to a method and apparatus for injecting molten material into a mold cavity, which is entitled " Method and Apparatus for Injecting a Molten Material into a Mold Cavity & May be used in conjunction with embodiments for controlling the molding process, such as disclosed in U.S. Patent No. 5,728,329 (Applicant's case 12467CC), which is incorporated herein by reference.

An embodiment of the present invention is directed to a molding process, such as disclosed in U.S. Patent No. 5,716,561, filed February 10, 1998, entitled " Injection Control System, " Which is hereby incorporated by reference.

An embodiment of the present invention is described in U.S. Patent Application No. 61/952281 entitled " Plastic Article Forming Apparatus and Methods for Using the Same " ), Which is hereby incorporated by reference. &Lt; RTI ID = 0.0 &gt; [0002] &lt; / RTI &gt;

An embodiment of the present invention is described in U.S. Patent Application No. 61/952283 entitled " Plastic Article Forming Apparatus and Methods for Using the Same " ), Which is hereby incorporated by reference. &Lt; RTI ID = 0.0 &gt; [0002] &lt; / RTI &gt;

It should be understood that the dimensions and values disclosed herein are not strictly limited to the exact numerical values listed. Instead, unless stated otherwise, each such dimension is intended to mean both an enumerated value and a functionally equivalent range near the value. For example, a dimension disclosed as "40 mm" is intended to mean "about 40 mm ".

All literature cited herein, including any cross-referenced or related patents or applications, and any patent application or patent claiming priority or claim of such application, are hereby expressly excluded or otherwise limited Are incorporated herein by reference in their entirety. The citation of any document is merely illustrative of the fact that it is a prior art to any invention disclosed or claimed herein, or that any such invention, either alone or in any combination with any other reference or reference, Nor does it acknowledge that it does so. Also, any meaning or definition of a term in this specification shall in any way conflict with any meaning or definition of the same term in the literature to which it is incorporated by reference, the meaning or definition given to that term in this specification shall prevail.

While particular embodiments of the invention have been illustrated and described, it will be apparent to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims (15)

As a method of automatically adjusting the injection molding process to compensate for the change in the flowability of the molten plastic material (reference numeral 1400 in FIG. 10, p. 40, lines 4 to 14)
(Step 10 in FIG. 1, page 14, line 8 to page 15, line 9) having at least one mold cavity (reference numeral 1410 in FIG. 10, page 40, 14 lines);
An injection molding controller (50 of FIG. 1; page 15, line 10 to page 17, see FIG. 1) including a pressure control output configured to provide a control signal at least partially determining an injection molding pressure for the injection molding process of the injection molding machine, 15, row 1420 in FIG. 10, line 4 to 14), the method comprising:
The method comprises:
Measuring the first control signal from the pressure control output at a first time during the injection molding cycle (reference numeral 1430 in FIG. 10; page 40, lines 4-14);
Measuring the second control signal from the pressure control output at a second time in the injection molding cycle following the first time (1440 in FIG. 10; p. 40, lines 4-14);
Comparing the first control signal from the pressure control output section with the second control signal from the pressure control output section to obtain a comparison result (reference numeral 1450 in FIG. 10; page 40, lines 4-14 ); And
Determining a third control signal for the pressure control output, based at least in part on the comparison result, at a third time subsequent to the second time (1460 of FIG. 10; Rows) of the &lt; RTI ID = 0.0 &gt;
Way. The method according to claim 1,
Wherein the determining comprises determining the third control signal at a third time that is within the same injection molding cycle as the second time
Way. 3. The method according to claim 1 or 2,
The third time being located within a subsequent molding cycle from the second time
Way. 4. The method according to any one of claims 1 to 3,
Determining a time difference between the first time and the second time,
Wherein the comparing comprises comparing the first control signal and the second control signal based at least in part on the time difference to obtain the comparison result
Way. 5. The method according to any one of claims 1 to 4,
Wherein the comparison result is a flow factor (FF) used as a soft sensor melt viscosity input to the controller, wherein the FF is determined by: &lt; RTI ID = 0.0 &gt;
FF = (CS1-CS2) / T
Here, CS1 is the first control signal,
CS2 is the second control signal,
T is the time difference between CS1 and CS2
Way. 6. The method of claim 5,
Wherein the third control signal is proportional to the flow coefficient
Way. 6. The method of claim 5,
T is about 1 millisecond
Way. 8. The method according to any one of claims 1 to 7,
The comparison result is used as a basis for a viscosity change index (VCI) used as a soft sensor melt viscosity input to the controller, the VCI being determined by the following equation:
VCI = (CS1 - CS2) / S
Here, CS1 is a first control signal,
CS2 is the second control signal,
S is the positional difference for the melt transfer machine component
Way. 9. The method of claim 8,
The third control signal is proportional to the VCI
Way. 9. The method of claim 8,
S is about 1 micron
Way. 11. The method according to any one of claims 1 to 10,
Wherein the step of comparing the first control signal with the second control signal includes comparing the first control signal and the second control signal with an optimal control signal based on an optimal pressure curve
Way. 12. The method according to any one of claims 1 to 11,
Wherein providing the injection molding machine comprises providing a melt transfer machine component,
Measuring a first position of the melt transfer machine component at the first time;
Measuring a second position of the melt transfer machine component at the second time;
Further comprising determining a position difference between the first position and the second position,
Wherein the comparing step includes comparing the first control signal and the second control signal based at least in part on the position difference to obtain the comparison result
Way. 13. The method according to any one of claims 1 to 12,
Further comprising the step of controlling said injection molding pressure by transmitting said third control signal to a melt pressure control device
Way. 14. A controller (50 of FIG. 1; page 15, lines 10 to 17, line 15) configured to perform the method of any one of claims 1 to 13. A molding machine (10 of FIG. 1, page 14, line 8 to page 15, line 9) comprising the controller of claim 14.

Images